In internal combustion engines, main crankshaft bearing assemblies typically each comprise a pair of half bearings retaining a crankshaft that is rotatable about an axis. Each half bearing is a hollow generally semi-cylindrical bearing shell and, typically in crank shaft journal bearing assemblies, at least one bearing shell is a flange half bearing, in which the bearing shell is provided with a generally semi-annular thrust washer extending outwardly (radially) at each axial end. In some flange half-bearings, a single-piece construction of the bearing shell and thrust washers is used, whilst in other half-bearings, the bearing shell and the thrust washer are loosely mechanically engaged with clip-like features, and in a further type of half-bearing the thrust washers are permanently assembled onto the bearing shell by deformation of engagement features. In other bearing assemblies it is also known to use an annular (circular) thrust washer.
Bearing bushes are used at the small end of a connecting rod, to connect the connecting rod onto the piston pin (also known as a gudgeon pin or wrist pin). Bearing bushes may also be used elsewhere in an engine. Bearing bushes are hollow cylindrical bearing liners, that may be solid sleeve bushes, split bushes (in which a strip is formed into a cylinder with butt-jointed ends) or clinch bushes (like split bushes, additionally provided with mutual engagement features on the ends of the strip).
Known bearing shells, thrust washer and bearing shell flanges have a layered construction, in which a substrate comprising a strong backing material is coated with one or more layers having preferred tribological properties to provide a bearing surface that faces a cooperating moving part, e.g. a crankshaft journal, in use. In known bearing shells, a substrate comprises a backing coated with a lining layer, and the substrate is in turn coated with an overlay layer.
The strong backing material may be steel, having a thickness of about 1 mm or more. A known lining layer may be a copper-based material (e.g. copper-tin bronze) or an aluminium-based material (e.g. aluminium or aluminium-tin alloy), which is adhered to the substrate (either directly to the backing or to an optional interlayer). The thickness of the lining layer is generally in the range from about 0.05 to 0.5 mm (e.g. 300 μm of copper-based alloy consisting of 8% wt Sn, 1% wt Ni, and balance of Cu, apart from incidentally impurities). The overlay layer may be 6 to 25 μm of a plastic polymer-based composite layer or a metal alloy layer (e.g. a tin-based alloy overlay).
Known bearing bushes comprise a strong steel backing layer and a lining layer on the backing layer, which provides the running surface for the journal (e.g. gudgeon pin/wrist pin) rotatably held in the bearing.
WO2010066396 describes a plastic polymer-based composite material for use as a bearing overlay layer on a copper- or aluminium-based lining layer, which is in turn bonded onto a steel backing. The described overlay layer comprises a matrix of a polyamide-imide plastic polymer material, having particulate distributed throughout the matrix.
Fuel-saving operating schemes have become popular for automotive engines, which increase the frequency with which the engine is started. Under a “stop-start” operating scheme, stopping and restarting vehicle movement also leads to the engine being stopping and restarted again. Under a “hybrid” operating scheme, the engine is turned off when the vehicle can be powered by an alternative power source, commonly being electrically powered. Whilst engine bearings are typically designed to last the life of the automotive vehicle, the greater frequency with which the engine is started under such operating schemes places an increased demand upon the performance of the sliding bearings by increasing the frequency with which bearing surfaces of the bearing shells, thrust washers and bearing bushes contact the journals of the crankshaft and gudgeon pin, and contact the counterfaces of the associated crankshaft web. However, increased contact causes correspondingly increased wear of the running surfaces of the bearing shells, thrust washers and bearing bushes.